Detecting mechanical indentation from the time constants of Li-ion batteries

Lithium-ion batteries pose severe hazards if their safety is compromised. Previous work has shown that mechanical damage to the battery may not affect its voltage, capacity, or other primary specifications. Therefore, currently, there is no method to check the integrity of battery cells inside an electric vehicle battery pack once it has been subjected to a shock or impact. Here, we report a method to detect mechanical damage to Li-ion cells from their electrical response. We formulate the distribution function of relaxation times (DRT) by a series of passive electrical elements consisting of inductors, resistors, and capacitors. Using our DRT formulation and criteria, we show that the indented cells have substantially different high-frequency time constant characteristics than the control group. This non-invasive method has the potential for detecting hazardous mechanical damage to the batteries of electric vehicles after a road crash or impact landings of drones.